Longshadow Loc: Audubon, PA, United States

I just worry about what I see with my 18-200; zoom (crop) until the composition looks good.
Not too worried about what focal length it winds up being; does it really matter as much as the end result?
I was weened on a "FF" camera.

speters Loc: Grangeville/Idaho

No, you are absolutely right, a 100mm lens will always be a 100mm lens no matter what camera you mount it on (you can't change its physics), but the field of view changes when put on cameras with different sensor sizes, and that's all there's to it, pretty simple!

Linda From Maine Loc: Yakima, Washington

I owned my first dslr (a crop sensor, aka APS-C) for four years before I ever heard the term and found out there was more than one sensor size (this was pre-UHH).

To the OP: you have what you have; look through the lens and see what you see. Ignore the voices in your head

Longshadow Loc: Audubon, PA, United States

User ID

True that, about pixel density. You ought to
begin a whole major thread on pixel density.

Now what about "crop" and "zoom" ? Many
inquiring minds really want to know !

.

anotherview Loc: California

Close. A cropped sensor (because physically smaller) records a smaller area of the field of view for a given lens.

Because of my limited understanding of optics, I hesitate to say more.

But from experience I can say that some concepts in photography elude quick understanding. The light bulb may take awhile to go on.

Keep at it for an answer that suits and satisfies you.

Bipod

A prime lens (or zoom at a particular focal setting) will have a certain actual focal length F and a certain
angle-of-coverage A. This is what the lens sees. The longer the focal length, the smaller the angle-of-coverage.

Every lens mount has a fixed flange-to-frame distance (FFD).

At a given FFD, a lens with angle-of-coverage A will project a circular image having
a diameter D (the image diameter).

The square or rectangular image sensor must fit within D.

Usually, the four corners of the sensor will touch or almost touch the image circle
having diameter D. If the sensor is smaller, it is a "crop sensor" camera: the angle-of-view
seen by the sensor will be smaller than the angle-of-coverage of the lens.

The term "crop sensor" is someone confusing, since the sensor isn't cropped: the image is.
The term is not used in optical engineering.

A given lens has a certain "resolving power": the abiliity to separatee fine detail.
The finest detail that can be separated is the resolution of the lens, which may vary
from one part of the projected image to another (usually the resolution is lower
off-axis).

The image sensor also has a certain resolving power, which is limited by many factors
in its construction, but primarily by pixel density. The total number of photocells is
the total potential resolution of the sensor. If it is color sensor, then it take three photocells
to produce one color "pixel".

The resolving power of a camera cannot exceed that of its lens. In other words, the
sensor captures the projected image. However, for good quality lenses at middle
appertures, the resolution of the projected image far exceeds that of the image sensor.
(were you to inspect the projected image with a loupe, you would see far more detail
than the camera will capture).

Any area within the image circle that does not fall on the sensor represents wasted
lens resolution.

On the other hand, if any or all of the corners of the sensor extend beyond the image
circle it creates hard vignetting. This represents wasted image sensor resolution.

It's easy to see that square frames represent a more efficient use of the projected image
than rectangular frames.

The maximum number of resolved details that the lens and sensor can capture is the
total resolution of the camera. It cannot exceed the number of "megapixels", but may
be far less. The light arriving at the lens contains a certain amount of information,
but this is decreased three first by the lens and second by the sensor.

Total resolution is imporant because it is fixed at exposure and cannot be increased.
However, many things that are done to an image file will decrease resolution: cropping,
some digital filters, lossy compression, printing, etc.

Focal lengths of lenses for crop-sensor cameras are often expressed in "35 mm equivalents",
so that a "normal" lens is still "50 mm", not something shorter.

Frames smaller than 35 mm have been in use for spy cameras (e.g., Minox) since 1936.
The were only used for amateur photography after Kodak introduced 110 cartridge film
in 1972. 110 film (13 mm x 17 mm format) was never used by professionals or serious
amateurs.

Today "small is the new large". Loaves of bread, tubs of yogurt, jars of fruit keep
getting smaller. Pretty soon a dozen eggs will be 11. No force in nature is as powerful
as marketing--it trumps math and physics every time!

If a manufacturer can sell you a unicycle for the price of a bicycle, it wins. To that end,
it will tell you that uniycles are new, improved, high-technology, more advanced, more
natural (like walking!), way cool, very trendy, all the hipsters are buying them, etc. So
of course they cost more than a regular bicycle....

"Ever get the feeling you've been cheated?" --John Lydon

Longshadow Loc: Audubon, PA, United States

A pound of coffee is now 12 ounces, as well as the cans of vegetables and condensed soups.

BebuLamar

The focal length multiplier, the crop factor and the 35mm focal length equivalent were introduced at the introduction of digital cameras with the assumption that most of the people who buy a digital camera would be familiar with the field of view certain focal length would have on the 35mm camera. That assumption may be true back then but today it's far from the truth. Without that assumed knowledge all those things are useless.

rmorrison1116 Loc: Near Valley Forge, Pennsylvania

Then it's not a pound. If the package is labeled 1 pound then there must be 16 ounces in it. I know what you mean though; for the price of what use to be a pound of coffee you now get 12 ounces. But, if you take it even farther back, for the price of 12 ounces today, at one time you could buy a whole barrel of coffee.

Bipod

There is a difference between raising the price (obvious to a buyer)
and sneakily reducing the size of the can (or giving a plastic tub or a
glass bottle a concave bottom, so it looks like it's the same size but holds less).

Being decpetive, sneaky and untruthful used to be shameful in the USA.
It isn't any more. The only shame is in getting caught!

Longshadow Loc: Audubon, PA, United States

What USED to be a pound of basically anything, including bacon...
But a pound of ground beef is ≈a pound.

The hopper

Thanks everyone - all good responses. I think I get it now. Perhaps Orrie Smith was correct in saying I was overthinking the problem!!!

SteveR Loc: Michigan

Jerry's illustration should help clear things up for you. A 100mm lens is ALWAYS a 100mm lens. It projects a circular image. A full frame sensor will capture a rectangular image that almosts fills that circular image, but some of the rounded portions of the image are left out. A crop sensor will capture a smaller rectangular image than the full frame's rectangular image. However....the image captured within the crop sensor's smaller rectangle is the same size a that same image within full frame's larger rectangle. The full frame's larger rectangle merely contains more extraneous image. The reason a 100mm may be said to appear to be a 160mm lens is that the image on the crop sensor has the "field of view" of a 160mm lens by "cropping" out the fuller image that the full frame sensor would have captured. It's why they are called "crop" cameras. The cropping is done "in camera." The same effect could be achieved by taking a full frame photo and cropping it down in p/p.

rmorrison1116 Loc: Near Valley Forge, Pennsylvania

Not so much as change the focal length.